Conventionally, there is a calculation theory called a first-principle calculation theory of estimating physical or chemical properties (hereinafter called properties) of a material according to a basic principle of quantum mechanics. As this kind of calculation theory, there is a calculation theory based on a density functional theory, in which properties, such as mechanical properties including elasticity, conductive properties including superconductive properties, a dielectric property and a magnetic property, are reproduced with relatively high accuracy, and a computation scale is in an implementable range. This calculation theory is already applied to material design, and there are numerous examples with its estimation accuracy verified through experiments (for example, see “Keisanki Material Design Nyumon (Introduction to computational material design)” edited by Hideaki Kasai, Hisazumi Akai, Hiroshi Yoshida, Osaka University Press (2005)).
As computation techniques based on a density functional method, a plurality of techniques are known, such as generalized gradient approximation (GGA), GW approximation, GW+Γ approximation and LDA+U approximation, regarded as techniques for solving problems caused by local density approximation (LDA).
However, each of the above-mentioned computation techniques has a problem of not giving a method for reaching a real solution (exact solution). In other words, until now, there is not a self-consistent calculation theory of reaching a real solution while a single-electron basis set being given by LDA in high accuracy is utilized.
On the other hand, the present inventor has proposed a fluctuation reference determination method as an effective many-electron calculation based on a multi-configuration reference density functional method (for example, see WO 2007/141942). With this method, an extended Kohn-Sham equation for reproducing a fluctuation variable (correlation function) having a positive definite property, such as local density fluctuations, in addition to one-electron density is given, whereby the reproduction accuracy of physical quantities can be raised to arbitrary accuracy. With this computation technique, total energy, one-electron density and a specific fluctuation variable of a material are reproduced simultaneously through the determination of the lowest energy state of a model Hamiltonian. Furthermore, by using a model system and its stable solution as initial values, a time-development equation for reproducing total energy, one-electron density and canonical correlation function is given, and a highly-accurate first principle electronic state computing method for reproducing the external field responses (responses to dynamic deformation and electromagnetic field application) of a material is given.
However, the effective many-electron computation based on the aforementioned multi-configuration reference density functional method is a computation technique that inevitably requires reference calculation, such as a Quantum Monte Carlo Method, a Transcorrelated Method, a Configuration Interaction Method, a Perturbation calculation/Green's function Method or an Effective Potential Method. For this reason, the reproduction accuracy of physical quantities depends on the calculation accuracy of the reference calculation, and a calculation technique reaching a real solution beyond the calculation accuracy of the reference calculation is not given.